Process for electroforming nickel containing dispersed thorium oxide particles therein

ABSTRACT

Nickel electroforming is effected by passing a direct current through a bath containing a dissolved nickel salt or a mixture of such salts, such as those present in sulfamate or Watts baths, and finely divided sol-derived thorium oxide particles of 75 to 300 Angstroms, preferably 100 to 200 Angstroms diameters therein, at a pH in the range of 0.4 to 1.9, preferably 0.8 to 1.3. The nickel so deposited, as on a pre-shaped stainless steel cathode, may be produced in desired shape and may be removed from the cathode and upon removal, without additional working, possesses desirable engineering properties at elevated temperatures, e.g., 1,500* to 2,200*F. Although the material produced is of improved high temperature stability, hardness and ductility, compared to nickel alone, it is still ductile at room temperature and has properties equivalent or superior to nickel at room temperatures up to 1,500*F. Further improvements in mechanical properties thereof may be obtained by working. Also disclosed are electrodeposition baths, methods for their manufacture and products resulting from the electrodeposition process.

United States Patent [191 Malone [451 May 13,1975

[75] Inventor: Glenn A. Malone, Williamsville,

[73] Assignee: Textron Inc., Providence, RI.

[22] Filed: May 10, 1974 [21] Appl. No.2 468,877

Related U.S. Application Data [63] Continuation-in-part of Ser. No.177,501, Sept. 2,

1971, abandoned.

[52] U.S. Cl. 204/3; 204/16; 204/49 [51] Int. Cl. C23b 7/08; C23b 7/00;C23b 5/08 [58] Field of Search 204/3, 4, 9, 16, 49

[56] References Cited UNITED STATES PATENTS 3,061,525 10/1962 Grazen204/16 FORElGN PATENTS OR APPLICATIONS 651,826 11/1962 Canada ..204/16602,099 7/1960 Canada ..204/16 OTHER PUBLICATIONS Products Finishing,August 1962, pgs. 62-64, 66, 68. Materials in Design Engineering, Sept.1962 pgs. 105-107. Modern Electroplating edited by Fred Lowenheim, 2ndEd. 1963 pgs. 260-265, 280-285.

Primary ExamineF-T. M. Tufariello Attorney, Agent, or FirmBean & Bean[57] ABSTRACT Nickel electroforming is effected by passing a directcurrent through a bath containing a dissolved nickel salt or a mixtureof such salts, such as those present in sulfamate or Watts baths, andfinely divided solderived thorium oxide particles of 75 to 300Angstroms, preferably 100 to 200 Angstroms diameters therein, at a pH inthe range of 0.4 to 1.9, preferably 0.8 to 1.3. The nickel so deposited,as on a pre-shaped stainless steel cathode, may be produced in desiredshape and may be removed from the cathode and upon removal, withoutadditional working, possesses desirable engineering properties atelevated temperatures, e.g., l,500 to 2,200F. Although the materialproduced is of improved high temperature stability, hardness andductility, compared to nickel alone, it is still ductile at roomtemperature and has properties equivalent or superior to nickel at roomtemperatures up to 1,500F. Further improvements in mechanical propertiesthereof may be obtained by working. Also disclosed are electrodepositionbaths, methods for their manufacture and products resulting from theelectrodeposition process.

19 Claims, N0 Drawings PROCESS FOR ELECTROFORMING NICKEL CONTAININGDISPERSED THORIUM OXIDE PARTICLES THEREIN This application is acontinuation-in-part of my application Ser. No. 177,501, filed Sept. 2,l97l, now abandoned.

This invention relates to the production of nickel having improvedproperties at high temperatures. More particularly, it relates to themaking by electroforming means of such nickels, which sometimes may beutilized directly, with no additional working or processing. Theinvention also relates to electroforming baths used in carrying out theprocess.

Electrodeposition of metals and alloys onto formed cathodes to producemetal items is known. The combining or alloying with nickel and othermetals of finely divided refractories, such as metal oxides, e.g.,thorium oxide, to improve the high temperature properties of the metals,has been successfully practiced, especially in recent years, because ofthe demands for high temperature-resistant structural materials for themaking of rocket engines, gun barrels and other parts of apparatusessubjected to the extraordinarily high temperatures utilized in moderntechnology. Dispersion strengthened nickel alloys have been produced inwhich zirconium oxide or thorium oxide, in monoclinic form, was mixedwith nickel as a very finely divided powder, hydrogen reduced to removenickel oxide, pressed and again hydrogen reduced. The describedsintering operation has been effected at an elevated temperature, about800C., and the alloys resulting are extruded or otherwise worked atelevated temperatures to improve their uniformity and physicalproperties. Also, metal oxides have been electrodeposited with nickel toimprove the strength of the nickel and to obtain better engineeringproperties for high temperature applications.

Although from the work summarized above it might appear that theproduction of improved high temperature nickel dispersion alloys byelectrolytic means could previously have been effected, the work of thepresent inventor has shown that this is not the case when especiallyadvantageous properties are desired in the nickel alloy without the needfor employing a combination of sintering and working operations. Thus,when the electroplating bath pH is in the range usual forelectrodeposition or electroforming solutions, or in the electroplatingrange usually employed, such as that of a Watts bath, defects appear inthe alloy upon heat ing and the improved properties of the alloydesigned to be built in by use of the refractory oxide are lost.However, by following the method of the present invention, with specialattention being given to keeping the pH in the very low range describedand of using ultrafine thorium oxide particles, which are obtained froma thoria sol or gel, stability of the alloy produced is improved andsuperior high temperature properties are obtained.

In accordance with the present invention a method of electroformingnickel containing thorium oxide particles comprises passing a directcurrent between an anode and a cathode in a bath containing a dissolvednickel salt and thorium oxide particles of particle sizes in the 75 to300 Angstrom diameter range at a pH in the range of 0.4 to 1.9 so as toform on the cathode a deposit of nickel containing dispersed thoriumoxide therein.

The electrolytic baths may contain any suitable source of nickel inionic form, obtainable from nickel chloride, nickel sulfate, mixtures ofnickel chloride and nickel sulfate, known as Watts baths, nickelsulfamate and other soluble nickel salts, preferably of strong acids.The concentrations of such salts in the aqueous medium of the bath,preferably water, is usually within the range of l to 60 oz. per gallon(0.7 to 40%, by weight), and is preferably of 3 to 36 oz. per gallon (2to 25%). When Watts baths are used they will usually contain from 3 to 8ounces per gallon of nickel chloride and 10 to 40 oz. per gallon ofnickel sulfate. Normally it will not be necessary to utilize additivesfor improving surface properties of the electrodeposited nickel alloybut if they are desired to be present they can be added withoutinterfering with the production of the nickel of improved hightemperature characteristics. Thus, minor proportions, generally from0.01 to 2 oz. per gal. of organic primary or secondary brighteners orother additives, such as quaternary pyridine salts, allyl sulfonicacids, lauryl sulfuric acids, the corresponding water soluble salts,e.g., sodium salts or chlorides, gelatin, gums or other surface activeagents or colloids and others of the large number of very well knownadditives of these types may be present.

In some cases, in addition to the nickel ions in the electrolyte, othersoluble ions may be present, such as aluminum, iron, copper, cobalt andsilver ions. Generally, the concentration of such ions in the bath willbe no greater than the content of nickel and preferably will be from 10to 40% thereof, if present at all. Thus,

' the alloys electrodeposited may include ultrafine thoria dispersoidsin nickel or ultrafine thoria dispersoids in a nickel alloy with anothermetal.

The very small thoria particles dispersed-in the electrolytic baths anddeposited with the nickel on the cathode by electrophoretic action maybe applied with another suitable hard and inert metal oxide which, byits presence, can improve the high temperature stability and propertiesof the resulting dispersion alloy, by interrupting fault lines in thealloy and preventing recrystallizations to weaker forms. Among theuseful oxides preferable are those of zirconium, aluminum, copper,

iron, titanium, zinc and silicon, but preferably thorium oxide isemployed alone. In the past, the oxides which were useable to producedispersoids in metals were limited by the availabilities of finelydivided powders for the sintering of mechanically mixed powders, withsubsequent working to produce the dispersion alloy. Now, however, withthe present process, wherein electroforming or electrodeposition from aliquid medium (highly preferably aqueous) is employed, it is possible toutilize sols or gels of thoria which are very finely divided oxides orhydrates thereof, convertible to the oxides in the electrolytic bath.Also, in addition to such gels based on thorium, aluminum, zirconium andsilicon gels are also obtainable and it is expected that others will beavailable in the future, capable of converting to oxides which aredepositable from electrolytic baths. Also, the gels may be dehydrated toproduce very small particles of the oxides, as sols, in which theparticles contain little or no water.

An exemplification of the thorium oxide gels or sols which are used isfound in the Journal ofAppIied Chemistry, Volume 17, May 1967, at pages147 to 150. De-

composition curves for the gel as a function of water removal withincreasing temperature are given, showing that the gel retains somewater at temperatures even as high as 900C. This makes the gel anunlikely source of thorium oxide for electrophoretic deposition in analloy wherein it is important that no water be present, since water inthe oxide particle usually causes severe weakening of the alloy as itseeks to escape when the temperature is raised. Similar considerationsmake the use of the other gels and sols appear unlikely for successfulproduction of dispersion hardened nickel or other metals or alloys. Yet,by the method of the present invention they have been successfully usedand help to make superior nickel electroforms.

With agitation in the electrolytic bath, as by ordinary mixing orblending means, the gel or other comparable form in which the refractorythorium oxide (with or without other metal oxide gel) is added to thebath is broken down so that the particle sizes thereof, aselectrophoretically or otherwise deposited with the nickel or nickelalloy on the cathode, are small and are evenly spaced, of sizes in the75 to 300 Angstroms range, preferably from 100 to 200 Angstroms andaveraging about 150 Angstroms. The figures given are preferred sizes forthorium dioxide (thoria) but also are often applicable when others ofthe mentioned oxides are codeposited. It is possible to use therefractory oxides as fine powders too but in gel, sol or other hydrousform they give best results. It is considered that superior results areobtained when the gel form is used and is converted to a sol during themaking of the electroforming bath. The products made are thought to besuperior to those made from finely mechanically divided (ball milled)particles of thoria because of the high surface areas of the solcrystallites, which have ten or more times the area of a sphere of thesame diameter, e.g., 10 to 1,000 times, preferably about 100 times.

The proportion of thorium oxide, utilized in the electrolytic orelectrodeposition bath will usually be from 0.1 to 10% of the nickel inthe bath, preferably from 0.5 to 5% and most preferably from 0.5 to 3%thereof. There is a relationship between the percentage of the oxide andits particle size and the proportion thereof deposited in the dispersiontype alloy. Generally, it is found that the weight percent of the oxidein the final alloy is less than the proportion in the electrolytic bath,usually from to 50% thereof and similar volume percentages also apply.Normally, the finest particles available will be employed, within theranges mentioned and in some cases, when possible, even smallercrystallites of thoria can be used. The smaller the crystallites themore crystallite embodiments or termination points there will be in thefinal alloy to prevent failures along fault lines and to interfere withundesirable recrystallizations. If other oxides are used with thoria thetotal metal oxide content should be in the previously mentioned 0.1 to10% range, by weight.

A very surprising feature of the present invention is the importance ofmaintaining the pH of the electrolyte, containing dispersoid material,at a highly acid value. This is so because it would be expected that useof acidic electrolyte would decrease the nickels strength and thereforewould be avoided. If the pH is in the range of about 0.4 to 1.9, gooddispersion of the crystallite oxide is obtained and surprisingly, thecontent of moisture, either free or chemically sorbed or attached to thecrystallites, is low. At higher pHs although good dispersions are madeand dispersion alloys are produced, it has been found that at the hightemperatures to which they may be subjected in use, e.g., from l,500 to2,200F.' and even higher, the alloys are weakened, apparently due to thefact that moisture is still contained in the crystallite and passesthrough the crystal structure, resulting in a brittle material of lowultimate strength. Preferred pl-ls for best results and strongest hightemperature nickel are within the range of 0.8 to 1.3 and it is morepreferable to operate at a pH of 0.8 to 1.], most preferably about 1.

Although it is not important how the pH is obtained (exceptacidification should be effected after addition of the crystalliteoxide) and various acidifying agents may be employed, it is preferredfor such agents to be acids which have a common anion with the saltsemployed in the electrolyte. Thus, hydrochloric acid or sulfuric acidmay be used to lower the pH of a Watts bath. Sulfamic acid and sulfuricacid may be employed together, sometimes with sulfonic acids, to lowerthe pH of sulfamate baths. Sometimes a commonality of anions will not bemaintained and then the usual acidifying agents may be used. Ordinarily,one will avoid employing strongly oxidizing acids, although they areoperative in various embodiments of the invention. It is preferred touse the strongest acids, such as hydrochloric acid, sulfuric acid,hydrobromic acid, phosphoric acid, and others of this well known classwhich are essentially 100% ionizable in aqueous solution. Generally,these will be inorganic acids although there is no prohibition againstusing organic compounds. In Watts baths H is preferred with HCl.

The electrolytic baths may be made by simple mixing techniques, aspreviously mentioned with respect to the addition ofa sol, gel, or othersuitable colloidal form of the crystallite oxide, followed byacidification. Preferably a gel or sol-gel system will be employed. Theamount of acid will be such as to obtain the desired pH and generallythis will be in the range of from 1 to 20 oz. of acid per gallon. Theacid may be added after the dispersion of the crystallite or before,depending on the technique which is found to yield the best dispersionand electroforming in a particular case but generally it is highlypreferable (to produce a high temperature strength product) to add itafter the dispersion of the crystallite or gel material in theelectrolyte.

The electrolytic bath may be of any useful operating temperature butusually will be at a temperature in the range of 30 or 40 to 70C.preferably 40 to 60C. The anodes and cathodes may be of any suitablematerial known in the nickel electroforming art but it is preferred toemploy rolled depolarized or sulfur depolarized nickel as the anode andstainless steel or similar material, to which nickel does not adherestrongly as the cathode. By use of a stainless steel cathode, previouslyshaped so as to produce a nickel electrodeposit of desired form, afterplating is completed the nickel may be removed from the cathode withoutdamage. It has been found that the electrodeposited nickel items of thisinvention even if electroformed to final shapes, have very good hightemperature properties, including stability, resistance to erosion andcorrosion, and strengths, including yield strength, and elasticity,which are far superior to those of conventionally electroformed nickelat such elevated temperatures. In cases where the final shapes are notcapable of being manufactured readily from worked and sintered orotherwise worked and formed alloys containing the present crystallites,and when the nickel alloy, as formed, is not as good as desired, thenickel alloys may be electroformed by the present methods on flatcathodes or on those with simple curves and may subsequently be worked,as by rolling, hammering, extruding or bending, for from 5 seconds to 1hour, to increase the degree of dislocation entanglement present in thealloy structure and further to improve the high temperature propertiesof i the product.

The speed of electrodeposition of the alloy is regulated by the passageof current through the electrolyte. Although various current densitiesmay be utilized, one should usually operate at current densities in therange of about 5 to 100 amperes per square foot, preferably about to 50amps/sq. ft.

The time of plating and the thickness of the electrodeposited alloy areinterrelated with the current flow. Generally, plating will be effectedin a period of 4 hours to 100 hours, usually from 6 hours to 24 hours.The thickness of alloy deposited will range from about 0.02 centimeterto 1 cm., with preferable ranges being from 0.1 to 0.6 cm., and often,most preferably from 0.2 to 0.4 cm. Electrodepositions may be effectedon cathodes from which the forms are removable or the nickel ofdescribed improved high temperature strength properties is formed ontofinal support materials, serving as cathodes. In the latter case suchsupporting material will normally be chosen so as to be capable ofresisting the high temperature to which it may be intended to subjectthe present nickel alloys.

After production of the dispersion alloy of desired thickness by themethod of this invention if there should be any water present in thethoria crystallites of the dispersed phase this may be removed to someextent and the product may be strengthened by a heat treatment at atemperature of about 500 to 1,000C. for a period of from 2 minutes to 24hours, usually from 1 to 5 hours, in which time some of the water willbe caused to escape from electrodeposited nickel. Preferably, if suchtreatment is effected, the alloy is worked for a period long enoughafter heating to allow rearrangement of the crystallites and the nickelto fill any voids which may be left due to driving off the water.Usually, the subsequent heat treatment is advantageously employed whenthe electrodeposition occurs at a pH of 2 to 5, preferably 2 to 4. Ofcourse, it is highly preferred not to have heat treat the formeddispersion alloys to remove water and it has been found that this isunnecessary when the processes of this invention are followed,especially when the electrodeposition takes place in the low pH rangesgiven. This is so despite the fact that the electrolyte may oftencomprise a major proportion of water and a gel or other material inwhich the thorium oxide is added or from which it is obtainable maycontain a similar high percentage of water. Preferably however, suchgels contain only minor proportions of water, usually from I to 40%,preferably from to 25%.

Other changes in the electroforming process may be desired to effectbest forming. For example, in some cases it may be desirable tointerrupt the current flow or even to reverse it or impose analternating current for a short period of time. If desired, the cathodemay be enclosed in a diaphragm to prevent any possible adverse effectson the forming from sludge or particulate impurities in the electrolyteor electroforming bath. ln

addition to agitating the bath, in some instances it may also bepreferred to maintain the cathodes in motion or to direct electrolyte inparticular flow patterns with respect to the cathodes. Temperatures ofthe composi- 5 tion may be varied during the electroforming operation,as may be the pHs, within the ranges given. Bath concentrations may bealtered and current densities can be changed to obtain best formingeffects, which are usually arrived at empirically. However, by followingthe methods described herein, improved electrodeposited dispersionalloys will be obtained, having better high temperature properties,e.g., strengths and stabililties.

The improved stabilities and strengths of the products of the inventionwill be such that the nickel alloys resulting, with about 0.2 to3.5%(anhydrous basis) of refractory oxide crystallite content, byweight, distributed fairly evenly throughout the alloys, will be capableof being employed at high temperatures, from 1 ,5 00 to 2,200F., andeven in many cases as high as 2,600F. for short time periods. Tensilestrenths are not decreased to the same degree as for pure nickel at temperatures up to 2,300F. Tensile strengths at a temperature of 2,000F.may be as high as 5,000 lbs./sq. in. and will usually be no lower than1,000 lbs./sq. in., even without subsequent treatments. With mechanicalworkings, the tensile strengths increase to as much as twice thesefigures. Nevertheless, it is often preferred to utilize the lowerstrength, unworked material because it does not require any additionalprocessing and is still of a sufficiently high strength to be employed.

The present invention seems to contravene some of the laws which hadpreviously been thought to apply to electrodepositions of dispersionalloys. In the acid baths, normally used at comparatively high acid pHs,water would be hydrolyzed to oxonium ions and such ions would charge therefractory oxide crystallites in the electrolyte. When hydrochloric acidwas employed as the acidifying means, the chloride ions would beabsorbed on the small crystallite primary adsorption sites and theoxonium ions would serve to screen the crystallites, giving thempositive charges. They would also mutually repel each other and aid indeflocculating the crystallites, which otherwise would be mutuallyattracted, in neutral solution, due to Van der Waals forces. With a muchmore acidic solution it would be expected that the screening effect ofthe oxonium ions would be insignifcant compared to the charges on ionsin the electrolyte and consequently, poor electrolytic deposition of thecrystallites would be anticipated, as well as some flocculation. Neitherof these disadvantageous results has been observed and the additionalunexpected advantage of lower moisture content of the crystallite in thealloy has been obtained, causing a great improvement of high temperaturestability of the dispersion alloys made.

Although use of the present invention greatly improves the properties ofthoria dispersion alloys at high temperatures and makes them easilymanufactured, it has been observed microscopically that even with fairlysmall thicknesses of the alloy being deposited, there is still somecolumnar growth which is not broken up as well as the crystallites as isdesirable. Work is being done to improve the deposition of thestrengthened nickel so as to increase even further the strengths andother useful properties of these products at high temperatures and ithas been found that best results are obtained'using the gel-derivedcrystallites in the 100 to 200 Angstrom particle diameter range at a pHabout 1, e.g., 0.8 to 1.3. Theoretically, according to this inventionlower pI-Is and lower particle sizes would be better but in practice thelower pHs are hard to maintain and lower particle size materials maytend to lump or aggregate.

The following examples will describe several preferred embodiments ofthe invention. All parts are by weight and all temperatures are in F.unless otherwise specified.

EXAMPLE 1 A Watts-type nickel electroforming bath is made by dissolving400 lbs. of nickel sulfate and 50 lbs. of nickel chloride in 100 gallonsof water in an electroforming tank. Then, after the salts are insolution, there are added to them 2 /2 lbs. of a dehydrated thoria gelcontaining about 21% of chemically sorbed water. This is mixed well intothe electrolyte and forms a sol of thoria crystallites of about 100 to200 Angstroms in diameter, averaging about 150 Angstroms. Next, the pHis adjusted by the addition of about 10 gallons of a 35% solution ofhydrogen chloride in water to produce a pH of about 1 in theelectrolyte. In the resulting electroforming bath the crystallites ofthe sol remain separated due to their positive surface charges.Uncharged particles tend to aggregate, which is objectionable and leadsto poor dispersion strengthening.

A plurality of nickel anodes and stainless steel cathodes, both havingtotal effective surface areas of about 10 sq. feet, is suspended in theelectrolyte. The cathodes are shaped as half cylinders, open sidesfacing the anodes so as to produce an electrodeposited dispersion alloyin the same shape. A direct current is imposed between the anodes andcathodes so that the current density is about 50 amps/sq. ft. Thepotential is maintained at 5 volts, the current flowing is about 500amperes and the bath temperature is 50C.

After 50 hours the current flow is interrupted and the electrodepositedspecimen is examined. It is found to be almost 0.3 cm. thick and evenlydeposited on the cathode. The electrodeposited half cylinder is removedfrom the cathode by known means and portions of it are cut for testingand for ultimate use as interior sections of a high temperatureprocessing vessel. One portion (A) is heated for hours at about 1,900F.and is then tested for tensile strength at 1,500F. Another portion (B)is tested at 1,500F. without previous heating. Still another part, thesame size as the other two, is mechanically worked by a combination ofhammering, extrusion and rolling, for a period of about 2 hours, afterwhich it is rolled to its original half cylinder form. The samples,designated A and B, respectively, compared to a control, C, of nickelformed without the refractory dispersed crystallite, are superior to thecontrol in ultimate strengths at elevated temperatures. The yieldstrengths, ultimate strengths and ductilities at room temperature andthe yield and ultimate strengths at 1,500F. are shown in the followingtable.

Ultimate strength 1,500F.)

The mechanically worked part has properties at least as good asspecimens A and B and is generally superior in room and high temperaturestrengths.

When employed in high temperature processing equipment which issubjected to shocks and strains during use, the electrodeposited nickelparts made according to this invention, whether heat treated or not andwhether worked or not, are of. satisfactory strengths, operating verysuccessfully at temperatures of 1,500F. Of special importance areimproved resistances to oxidation and increased yield and ultimatestrengths at the elevated temperatures mentioned. In the sameapplication at such temperature ordinary nickel units fail andelectrodeposited half cylinders made in the same manner but at a pH of4.0, without subsequent controlled driving off of water present in theelectroform also fail, apparently due to water escaping from them.

When the above experiment is repeated with nickel sulfamate or nickelchloride baths, similar results are obtained. In both cases, the nickelconcentration in the electrolyte is kept the same. Also, when minorproportions of other of the previously mentioned refractory metaloxides, e.g., copper, zirconium, aluminum, titanium, magnesium and ironin gel or dehydrated gel form or otherwise similarly finely dividedpositively charged particles, are employed with the thoria atconcentrations of 10 to 20% of the thoria concentration, improvedproperties of the electrodeposited nickel also result. I

When allyl sulfonic acid or quaternary pyridinium compounds are added asbrighteners or surface characteristic modifiers in the proportionspreviously described, they do not interfere with the electrodepositionof the dispersion alloy nor do they diminish the desirable propertiesobtained, and they help to improve lustre and appearance.

Following the procedure of this example, variations are made in currentdensity, electrolyte concentration, percentage of dispersed phase, timeof operation and shape of cathodes, with the results obtained beinguseful and superior to those for an ordinary electroformed nickelproduct. In some such cases, the deposited nickel alloy is not removedfrom the cathode but is utilized bound to it. In other applications,additional materials are coated onto the surface of the deposited alloy,e.g., dispersion alloys of chromium. In other cases, theelectrodeposited materials are ground and subsequently are sintered byconventional dispersion alloy manufacturing method. In such instances,the product obtained is superior to a control nickel alloy in itsresistance to high temperature oxidation and in its maintenance of goodyield and ultimate strength properties at elevated temperatures.

EXAMPLE 2 Panel specimens like those of Example 1 are produced byelectrolysis of a Watts bath but the deposits obtained, due to the shapeof the cathode, are flat. Electrolysis is discontinued after about 24hours, with the thickness of the nickel alloy produced being about 0.06cm. The bath used contains no boric acid but in another run, boric acidis employed, to the extent of 30 lbs. in the 100 gallons of water. ThepH is not affected much, being about 0.9 in such case. The productsobtained, using boric acid in the Watts bath, are of essentially thesame properties as those from the bath containing only nickel chlorideand nickel sulfate, with or without acidifying acid (HCl or H 80 inamount to yield the desired pH.

After removal of the electroformed nickel alloy from the cathode it istested by comparison to a control in the manner described in Example 1,but at 2,000F. The ultimate strengths of the experimental material andthe control (electroformed under the same condi tions but without thethoria gel and resulting dispersed crystallites) are about the same butthere is a significant improvement in yield strength, the control havinga yield strength of 1,900 lbs/sq. in. but the experimental specimenhaving a yield strength approximately 50% better, 2,800 lbs/sq. in.Furthermore, the dispersion strengthened specimen has the yield strengthand ultimate strength thereof improved by cold working, as by flexing,hammering, extruding, elongating and compressing for periods up to twohours at about room temperature. Similar treatments do not improve thepure or control electroformed nickel so as to increase its yield andultimate strengths at the high temperatures of use and testingdescribed.

EXAMPLE 3 Baths containing about 1,500 lbs. of nickel per 1,000 gallonsof electrolyte are made in which there are present 20 lbs. of hydratedthoria gel (about 20% B of particle sizes in the 75 to 300 Angstromrange. The dispersed oxide material is kept suspended by means of a pumpand circulator, which operate at low liquid velocities. The nickel inthe bath is obtained from nickel chloride, nickel sulfate and nickelchloride, or nickel sulfamate, but other nickel salts may also beemployed and the nickel may be added to the bath as the hydroxide,oxide, or in other suitable form, so long as it is then dissolved in theelectrolyte.

Electroformings are effected at various current densities, ranging fromto 50 amperes/sq. in. with plating times being from 1 hour to 100 hoursat room temperature so that the deposits range from 0.02 to 0.6 cm. inthickness. Voltages are preferably held at about 5 volts, althoughvoltage changes of fi0% are also effected during the platings. Currentdensities are preferably held about 5 to 30 amperes/sq. in. Conventionalbrightening and surface active agents are usually employed but in somecases are omitted. In some control experiments pHs are allowed to be ashigh as 3.5-5.

When the baths are at the higher pHs, e.g., 3.8, 4.5, the strengths (at1,500F. and higher) of the alloys produced are not as high as when thelower phs of this invention are employed. It is considered this is dueto the entrapment of water in the alloy matrix or in the crystalliteparticles.

The electroforms obtained, with the dispersed oxide crystallite therein,are readily removable from the cathodes and, when tested at hightemperature, show improved yield strengths, compared to pureelectroplated nickel. Furthermore, cold working improves the yieldstrength even further, which improvements are not obtained with ordinarynickel. This is also the case when the plating bath concentration ofnickel is changed i50% and when concentrations of the dispersed thoriaare changed similarly, but not necessarily concurrently with the changein the concentration of nickel ion. Instead of thoria-containingdispersion strengthened nickel, other analogous products based on copperoxide, zirconia and alumina may be made by the same methods but thethoria-nickel products are considered superior due largely to theirsignificantly improved high temperature properties previously mentioned.

EXAMPLE 4 The following experiment describes the electroforming ofnickel with thoria particles of different sizes codeposited with thenickel being plated, in an effort to strengthen it for use in hightemperature applications. Such dispersion strengthening is differentfrom dispersion alloying wherein hard particles are deposited with asofter metal matrix so as to increase its hardness and wear resistance.It has been found that particle size is not as critical in such type ofalloying as it is in dispersion strengthening applications. Thoria canbe electrodeposited with nickel or other metal and result in noimprovement in mechanical strength at elevated temperature. To bedispersion strengthened, the nickel or other metal should haverecrystallization inhibited at temperatures approaching the meltingpoint of the metal. Thus, the inert dispersoid particles should act toblock the movements of dislocations within the crystal latticestructure, increasing resistances to stress rupture and impartingincreased strength to the material when it is subjected to slip (stressin loading) or climb (recrystallization and grain growth in annealing).The characteristics of electrodeposits can be evaluated by comparingmicrostructures and measuring mechanical properties against controls.Thus, the importances of the size of the dispersoid particles andelectrolyte pl-l can be assessed.

To prove the effect of particle size of thorium oxide particles thereare tested three different sizes of thoria, (a) 5 microns diameter andlarger; (b) 0.6 to 0.8 microns (Fisher Sieve size), the finest ballmilled product available for these experiments; and (c) 0.01 to 0.02

micron (in sols produced from gels). The electroforming conditions areas follows:

Bath type Sulfamate Voltage 4-5 Current density 30 a.s.f

Percent thorium oxide in bath 0.5

Bath temperature F.

Anode Rolled, depolarized nickel Cathode Stainless steel Anode-cathodedistance 8 inches, average Forming rate 0.00l in./hr.

an angle less than 90. Photomicrographs at 100 times magnification showthe structure of this product to be of a fine columnar nickel graintypical of sulfamate and Watts type electrolytes, with surfaceirregularities apparently due to agglomeration of uncharged particles.The deposit is rough and a similar rough deposit results when micronparticles were used. After heat treating for 1 hour at 1,800F., invacuum, the material recrystallizes and the thoria particles outgasseverely, leaving voids and a porous structure. Such voids arenonuniform, showing that the uncharged thoria particles do not deposituniformly in the electroform. All these characteristics areobjectionable and it is evident that this material is unsatisfactory foruse at 1,500F. or any similar elevated temperature.

In the run utilizing the 0.01 to 0.02 micron thoria, charged to theelectroforming baths as a hydrated gel (containing about 21% water) andconverted therein to a sol, plating can be effected to a greaterthickness, and an electroform 0.050 inch thick is made and tested. As isshown by a photomicrograph thereof at 100 times magnification, thenickel-thoria electroform exhibits a typical columnar grain structurewhich, even after a thermal treatment at 2,300F. for 1 hour, does notundergo recrystallization. It is concluded that the presence of the veryfine particles, within the 75 to 300 Angstrom diameter range, inhibitsrecrystallization and results in dispersion strengthening of the nickel.Similar resistance to recrystallization is obtained at 1,500F. Inanother experiment, utilizing essentially the same conditions, but withincreased thoria content in the bath a 0.048 inch thick electroform ismade containing about 1.8% by weight of thorium oxide, the particlesthereof being those obtained from a 0.01 to 0.02 micron diameter thoriaso]. The electroform is reduced by cold working from about 0.048 inch toabout 0.024 inch in thickness, approximately equally in four workingpasses through cold working rolls, followed by stress relieving eachtime. Normally, under such conditions any cold worked metal will undergohigh angle grain growth and there will be a severe loss of strength whenit is subjected to thermal treatment in the annealing temperature range(the stress relieving treatment). However, the described electroformundergoes almost no recrystallization and the stronger cold workstructure thereof is retained. The annealing is to a temperature ofabout 1,800 to 2,000F. after each cold working. The small grain sizeresulting is unexpected and is attributed to the small particle sizes ofthe dispersoid and the exceptionally good dispersion thereof in thenickel matrix. Mechanical tests at 1,500F. on this material show that ithas a yield strength in excess of 16,000 p.s.i., more than double theultimate strength of pure nickel at this test temperature.

When the above-described experiments are run using other particle sizeswithin the 75 to 300 Angstrom diameter range, at pHs of 1.1, 1.0 and0.9, at temperatures of 30 to 70C., with thoria concentrations of 0.5 to5%, preferably 0.5 to 3%, of the nickel present, to plate outelectroforms of thicknesses from 0.03 to 1 cm. thick, preferably 0.1 to0.5 cm., similar increases in high temperature strengths are obtained,with even greater increases resulting at these lower pHs.

When similar experiments are run in which the electroforming bath pH isvaried to be inside and outside the 0.4 to 1.9 range a significantchange in ultimate strength of the electroform resulting is noted, whichis illustrated in the following table.

in improved ultimate strength at elevated temperature, despite the factthat the lower pH also results in a decrease in the thorium oxidedeposited. When the pH is held at 4.0 the electroform fails in a brittlefracture mode at an ultimate strength below that of pureelectrodeposited nickel but when the pH is maintained lower than thevalues given in the above table, e.g., l .2, 1.1, 1.0 and 0.9, theultimate strength is greater than that of pure nickel (which is about7,000 p.s.i.) and in the 0.8 to 1.3 pH range can be greater than 11,000p.s.i. Because greater deposits of the thoria are obtained at higher pHsit would have been expected that, in the absence of the desorptionphenomenon or other reason for the observed results, one would usehigher pHs to improve product strength. Therefore, the present resultsare unexpected.

From the above description and the specific examples given it is seenthat this invention represents a significant advance in the art ofmanufacturing dispersion strengthened nickel. Accordingly, the inventionis to be construed as covering the described subject matter and thosemodifications thereof wherein equivalents or substitutes are employed,without going beyond the inventive concept.

What is claimed is:

1. A method of electroforming dispersion strengthened nickel containingdispersed ultrafine thorium oxide particles, which electroformed nickelis of improved high temperature properties, which comprises passing adirect current between an anode and a cathode in an electroforming bathcontaining a dissolved nickel salt and 0.1 to on the basis of thedissolved nickel present, of thorium oxide particles of diameters in therange of 75 to 300 Angstroms, and at a pH in the range of 0.4 to 1.9,which electroforming bath contains ultrafine thorium oxide particlesobtained by admixing a thorium oxide sol or a hydrated thorium oxide gelwith an aqueous medium to produce a sol, so as to form on the cathode adeposit of nickel containing the dispersed ultrafine thorium oxideparticles therein, which nickel deposit is mechanically deformable atroom temperature and of improved high temperature strength compared toordinary electroformed nickel.

2. A method according to claim 1 wherein the bath is aqueous andcontains a source of nickel selected from the group consisting of nickelsulfamate, nickel chloride, nickel sulfate and a mixture of nickelchloride and nickel sulfate, the content of thorium oxide particlestherein is from 0.5 to 5% of the dissolved nickel present, the bath isat a temperature in the range of 30 to 70C. and the forming is continuedfor a period of time long enough to form a thickness of dispersionstrengthened nickel from 0.02 to 1 cm., with thorium oxide particlesdistributed therein.

3. A method according to claim 2 wherein the bath contains from 3 to 36oz. per gallon of a mixture of nickel chloride and nickel sulfate,nickel chloride or nickel sulfamate at a pH of from 0.8 to 1.3 and is ata temperature in the range of 40 to 60C., electroforming is continuedfor a time long enough to form a thickness of nickel from 0.02 to 0.6cm. thick with thorium oxide particles distributed therein, and theelectroforming is effected on a cathode from which the nickel containingdispersed thorium oxide particles is readily removable.

4. A method according to claim 3 wherein electroforming is effected on astainless steel cathode of a shape corresponding to that of a desiredfinished piece so that additional shaping of the nickel is minimized.

5. A method according to claim 3 wherein after forming of the nickelcontaining dispersed thorium oxide particles the electroform is workedmechanically to increase its high temperature strength.

6. A method according to claim 3 wherein the electroforming bath is anaqueous bath of the Watts or sulfamate type.

7. A method according to claim 3 wherein the thorium oxide particles arecharged to an electroforming bath as a sol or hydrated gel containingfrom 1 to 40% of chemically sorbed water.

8. A method according to claim 7 wherein the electroforming bath isacidified to a pH of 0.8 to 1.3 after charging of the thorium oxide.

9. A method according to claim 8 wherein the nickel containing dispersedthorium oxide crystallite particles is electroformed onto a cathode of ashape corresponding to that of the desired finished piece and theelectroformed nickel is removed therefrom.

10. A method according to claim 8 wherein the electroforming is effectedon a stainless steel cathode and the electroformed nickel containingdispersed thorium oxide crystallite particles is removed from thecathode and is mechanically worked to increase its high temperaturestrength.

11. An electroforming bath comprising a dissolved nickel salt andundissolved thorium oxide particles therein, at a pH in the range of 0.4to 1.9, with the thorium oxide particles being of particle sizes ofdiameters in the 75 to 300 Angstrom range and being sufficientlysuspended in the bath so as to form on a cathode a deposit of nickelcontaining dispersed thorium oxide when a direct current is passedthrough the bath, which deposit is of improved high temperaturestrength.

12. An electroforming bath according to claim 11 wherein the nickel saltis nickel sulfamate, nickel chloride, nickel sulfate or a mixture ofnickel chloride and nickel sulfate, the thorium oxide particles arethose obtained by admixing a hydrated thorium oxide gel with an aqueousmedium and are present to the extent of from 0.5 to 5% of the dissolvednickel present and the bath is at a temperature in the range of about 30to 70C.

13. An electroforming bath according to claim 12 wherein the nickel saltconcentration is from 3 to 36 oz. per gallon of a mixture of nickelchloride and nickel sulfate, nickel chloride or nickel sulfamate, thebath is aqueous, at a pH of from 0.8 to 1.3, at a temperature in therange of 40 to 60C. and the thorium oxide particles are of a size offrom about 100 to 200 Angstroms in diameter and are present to theextent of from 0.5 to 3% of the dissolved nickel present, which bath isacidified to a pH of 0.8 to 1.3 after incorporation therein of thethorium oxide particles.

14. An electroforming bath according to claim 13 wherein the thoriumoxide particles are crystallites of particle sizes of a diameter ofabout 150 Angstroms.

15. An electroforming bath according to claim 14, of the Watts orsulfamate type.

16. A method of making a nickel electroforming bath which comprisesadmixing with an aqueous solution of a nickel salt of the nickelsulfamate, nickel chloride, nickel sulfate, or mixed nickel chloride andnickel sulfate type, 0.1 to 10% on the basis of dissolved nickelpresent, of particles of thorium oxide, as a sol or a hydrated gel whichforms a sol thereof therein and adjusting the pH of the bath to a valuein the range of 0.4 to

17. A method according to claim 16 wherein the admixing is effected at atemperature of 40 to 60C., the particles of thorium oxide are ofdiameters in the range of from to 300 Angstroms and the electroformingbath is an aqueous bath containing from 3 to 36 oz. per gallon of amixture of nickel chloride and nickel sulfate, nickel chloride or nickelsulfamate at a pH of from 0.8 to 1.3.

18. A method according to claim 17 wherein the thorium oxide particlesare crystallites of particle sizes in the range of to 200 Angstroms andare admixed 'with a sulfamate or Watts-type nickel electroforming 19. Aproduct of the process of claim 1.

1. A METHOD OF ELECTROFORMING DISPERSION STRENGTHERNED NICKEL CONTAININGDISPERSED ULTRAFINE THORIUM OXIDE PARTICLES, WHICH ELECROFORMED NICKELIS OF IMPROVED HIGH TEMPERATURE PROPETTIES, WHICH COMPRISES PASSING ADIRECT CURRENT BETWEEN AN ANODE AND A CATHODE IN AN ELECROFORMING BATHCONTAINING A DISSOLVED NICKEL SALT AND 0.1 TO 10%, ON THE BASIS OF THEDISSOLVED NICKEL SALT AND 0.1 TO 10%, ON THE BASIS OF THE TERS IN THERANGE OF 75 TO 300 ANGSTROMS, AND AT A PH IN THE RANGE OF 0.4 TO 1.9,WHICH ELECTROFORMING BATH CONTAINS ULTRAFINE THORIUM OXIDE PARTICLESOBTAINED BY ADMIXING A THORIUM OXIDE SOL OR A HYDRATED THORIUM OXIDE GELWITH AN AQUEOUS MEDIUM TO PRODUCE A SOL, SO AS TO FORM ON THE CATHODE ADEPOSIT OF NICKEL CONTAINING THE DISPERSED ULTRAFINE THORIUM OXIDEPARTICLES THEREIN, WHICH NICKEL DEPOSIT IS MECHANICALLY DEFORMABLE ATROOM TEMPERATURE AND OF IMPROVED HIGH TEMPERATURE STRENGTH COMPARED TOORDINARY ELECTROFORMED NICKEL.
 2. A method according to claim 1 whereinthe bath is aqueous and contains a source of nickel selected from thegroup consisting of nickel sulfamate, nickel chloride, nickel sulfateand a mixture of nickel chloride and nickel sulfate, the content ofthorium oxide particles therein is from 0.5 to 5% of the dissolvednickel present, the bath is at a temperature in the range of 30* to70*C. and the forming is continued for a period of time long enough toform a thickness of dispersion strengthened nickel from 0.02 to 1 cm.,with thorium oxide particles distributed therein.
 3. A method accordingto claim 2 wherein the bath contains from 3 to 36 oz. per gallon of amixture of nickel chloride and nickel sulfate, nickel chloride or nickelsulfamate at a pH of from 0.8 to 1.3 and is at a temperature in therange of 40* to 60*C., electroforming is continued for a time longenough to form a thickness of nickel from 0.02 to 0.6 cm. thick withthorium oxide particles distributed therein, and the electroforming iseffected on a cathode from which the nickel containing dispersed thoriumoxide particles is readily removable.
 4. A method according to claim 3wherein electroforming is effected on a stainless steel cathode of ashape corresponding to that of a desired finished piece so thatadditional shaping of the nickel is minimized.
 5. A method according toclaim 3 wherein after forming of the nickel containing dispersed thoriumoxide particles the electroform is worked mechanically to increase itshigh temperature strength.
 6. A method according to claim 3 wherein theelectroforming bath is an aqueous bath of the Watts or sulfamate type.7. A method according to claim 3 wherein the thorium oxide particles arecharged to an electroforming bath as a sol or hydrated gel containingfrom 1 to 40% of chemically sorbed water.
 8. A method according to claim7 wherein the electroforming bath is acidified to a pH of 0.8 to 1.3after charging of the thorium oxide.
 9. A method according to claim 8wherein the nickel containing dispersed thorium oxide crystalliteparticles is electroformed onto a cathode of a shape corresponding tothat of the desired finished piece and the electroformed nickel isremoved therefrom.
 10. A method according to claim 8 wherein theelectroforming is effected on a stainless steel cathode and theelectroformed nickel containing dispersed thorium oxide crystalliteparticles is removed from the cathode and is mechanically worked toincrease its high temperature strength.
 11. An electroforming bathcomprising a dissolved nickel salt and undissolved thorium oxideparticles therein, at a pH in the range of 0.4 to 1.9, with the thoriumoxide particles being of particle sizes of diameters in the 75 to 300Angstrom range and being sufficiently suspended in the bath so as toform on a cathode a deposit of nickel containing dispersed thorium oxidewhen a direct current is passed through the bath, which deposit is ofimproved high temperature strength.
 12. An electroforming bath accordingto claim 11 wherein the nickel salt is nickel sulfamate, nickelchloride, nickel sulfate or a mixture of nickel chloride and nickelsulfate, the thorium oxide particles are those obtained by admixing ahydrated thorium oxide gel with an aqueous medium and are present to theextent of from 0.5 to 5% of the dissolved nickel present and the bath isat a temperature in the range of about 30* to 70*C.
 13. Anelectroforming bath according to cLaim 12 wherein the nickel saltconcentration is from 3 to 36 oz. per gallon of a mixture of nickelchloride and nickel sulfate, nickel chloride or nickel sulfamate, thebath is aqueous, at a pH of from 0.8 to 1.3, at a temperature in therange of 40* to 60*C. and the thorium oxide particles are of a size offrom about 100 to 200 Angstroms in diameter and are present to theextent of from 0.5 to 3% of the dissolved nickel present, which bath isacidified to a pH of 0.8 to 1.3 after incorporation therein of thethorium oxide particles.
 14. An electroforming bath according to claim13 wherein the thorium oxide particles are crystallites of particlesizes of a diameter of about 150 Angstroms.
 15. An electroforming bathaccording to claim 14, of the Watts or sulfamate type.
 16. A method ofmaking a nickel electroforming bath which comprises admixing with anaqueous solution of a nickel salt of the nickel sulfamate, nickelchloride, nickel sulfate, or mixed nickel chloride and nickel sulfatetype, 0.1 to 10% on the basis of dissolved nickel present, of particlesof thorium oxide, as a sol or a hydrated gel which forms a sol thereoftherein and adjusting the pH of the bath to a value in the range of 0.4to 1.9.
 17. A method according to claim 16 wherein the admixing iseffected at a temperature of 40* to 60*C., the particles of thoriumoxide are of diameters in the range of from 75 to 300 Angstroms and theelectroforming bath is an aqueous bath containing from 3 to 36 oz. pergallon of a mixture of nickel chloride and nickel sulfate, nickelchloride or nickel sulfamate at a pH of from 0.8 to 1.3.
 18. A methodaccording to claim 17 wherein the thorium oxide particles arecrystallites of particle sizes in the range of 100 to 200 Angstroms andare admixed with a sulfamate or Watts-type nickel electroforming bath asa thorium oxide aqueous gel or sol, after which acidification to thedesired pH is effected with hydrochloric acid.
 19. A product of theprocess of claim 1.